1. Field of the Invention
The present invention relates to a syringe assembly and more particularly concerns a syringe assembly having a flexible cover for blocking the transfer of fluids and particulate matter between the inside of the syringe barrel and the environment.
2. Description of Related Information
Generally speaking, a syringe assembly consists of a cylindrical barrel, most commonly made of thermoplastic material or glass, with a distal end adapted to be connected to a hypodermic needle assembly or other fluid transfer or fluid collection means. A proximal end of the barrel is adapted to receive a stopper and plunger rod assembly. One of the purposes of the stopper is to provide a relatively air-tight seal between itself and the syringe barrel so that movement of the stopper up and down the barrel will cause liquid, blood or other fluids to be drawn into or forced out of the syringe through the distal end. The stopper is moved along the syringe barrel by applying axial force to a rigid plunger rod which is connected to the stopper and is sufficiently long to be accessible outside of the barrel.
Hypodermic needle assemblies, tubing sets, stopcocks, valves and other fluid transfer devices are oftentimes removably attached to syringes for performing a variety of tasks such as: delivery of medication into patients and into devices; withdrawing fluid samples from fluid sources for subsequent delivery into a patient; and withdrawing fluid samples from patients. Usually the hub of the hypodermic needle assembly or other fluid transfer device has a tapered interior surface adapted to engage the tapered tip of the syringe barrel so that the two components are joined in a frictional interference fit. The tapered tip and the complimentary tapered receptacle and the hub are referred to as standard luer fittings. A wide variety of devices such as stopcocks and tubing sets have standard luer fittings which allow them to be engaged to a syringe tip.
Syringes may also be provided with a compression spring positioned between the proximal flange on the plunger rod and the barrel of the syringe for biasing the stopper toward the open end of the barrel. Such an arrangement is taught in U.S. Pat. No. 3,905,521 to Mead et al. Such an arrangement allows the compressed spring to provide a biasing force on the plunger rod and the stopper to create a lower than atmospheric pressure inside the barrel. This structure is useful for using the syringe as the dispenser, as taught by Mead et al., and also for using the syringe as a source of negative pressure, for example, in wound drainage setups wherein the wound is connected to the syringe through a tubing so that a lower than atmospheric pressure is constantly applied through the tubing to the wound.
Syringes are usually provided in an individual sterile package which is opened at the time of use. When the syringe is removed from the sterile package it may no longer be in a sterile environment. Accordingly, particulate matter and even bacteria in the environment may enter the syringe barrel through the proximal open end. After removal from the sterile package, a hypodermic needle assembly may be attached to the tip of the syringe barrel and then the syringe and needle assembly is used to pierce a medication vial whereupon the medication, which will be injected into the patient, is drawn into the syringe by moving the plunger rod distally with respect to the barrel. The syringe and hypodermic needle assembly are now ready to use for administering medication to the patient. Many hospitals enploy drug distribution systems wherein syringes are filled with medication in the hospital pharmacy using a laminar flow hood which produces a sterile environment for the filling operation.
However, many times syringes are used in procedures wherein the plunger rod and stopper may be repeatedly drawn back and forth along the barrel while the syringe is in a non-sterile environment. Each cycling of the stopper along the barrel provides potential for contamination of the liquid contained within the syringe barrel and/or the escape of a portion of that liquid.
Syringes are often used in procedures where the syringe assembly is used as a pump or an intermediate container for liquid and the stopper is cycled many times along the syringe barrel during the procedure. This type of use of a syringe, especially in a non-sterile environment, presents an increased risk of contamination of the liquid or escape of the liquid from the stopper. Pharmacy departments in hospitals frequently draw medication from a sealed vial into a large syringe and then pump the medication from this large syringe into smaller syringes to facilitate unit dose distribution programs. Also, certain surgical procedures provide for the injection of saline solution or other therapeutic liquid into the patient's vascular or arterial system. These procedures involve a stopcock and syringe assembly wherein the syringe barrel is withdrawn to draw saline solution from a reservoir into the syringe barrel and then the position of the stopcock valve is changed so that forward motion of the stopper along the syringe barrel forces the saline solution into the patient's artery. This procedure can be repeated several times during the procedure and presents an opportunity for particulate matter in the environment to be transferred to the injecting liquid.
U.S. Pat. No. 4,030,498 to Tompkins teaches the desirability of providing structure to prevent the contamination of medication or, in the alternative, where the syringe may contain potentially hazardous substances, to prevent contamination of the user and the environment. To this end, Tompkins teaches a contamination resistant syringe having two sealing rings which are axially spaced from each other. The sealing rings are prevented from sweeping the same area, inside the syringe barrel, and there is no communication between the chamber defined by the two sealing rings and the discharge area forward of the innermost sealing ring. Tompkins teaches that, in this manner, contamination which might enter from the rear of the barrel will be prevented from contact with the inner sealing ring and therfore contact with the medication. The syringe taught by Tompkins has deficiencies in that it is more expensive to manufacture because the barrel and plunger rod must be longer than the standard plunger rod and barrel and dual sealing rings must be provided. Also, an apparently larger syringe, as taught by Tompkins, may not be compatible with the large number of syringe devices which have been developed over the period of many years to accommodate standard size syringes. Accordingly, the user may be faced with a syringe which is incompatible with the other fluid delivery equipment.
The transfer of liquid to and from the syringe assemblies and structure for making the syringe more resistant to contamination have been addressed by the prior art, as alluded to above. However, there is still a need for a simple, straight-forward, reliable, easily fabricated standard size syringe with features for helping to prevent the transfer of fluid and particulate matter between the chamber in the syringe and the environment.